[processor/k8sattributes] Use the already available internal docker.ParseImageName function

[TylerHelmuth]

          Should we use the already available internal [docker.ParseImageName](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/internal/common/docker/images.go#L23) function instead?

I would prefer to all components use the same strategy for common functionalities. Note that the shared function cannot parse images with digest at the moment and should be fixed beforehand: #36279

Originally posted by @rogercoll in #36145 (comment)

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